1. Field of the Invention
The present invention relates generally to systems for initiating braking at the rear of a railway train. More particularly, the present invention relates to an invention which utilizes an air sensor to detect passage of air through an exhaust port of a brake pipe vent valve for the purpose of initiating braking at the rear of a train.
2. Description of the Prior Art
Many railway vehicles in service today utilize an air brake system whereby brake mechanisms on individual cars are actuated by selected pressure variations within a brake pipe extending the length of the vehicle. Typically, braking is initiated by an operator in the locomotive operating a brake valve which exhausts air within the brake pipe to atmosphere. The concomitant reduction in brake pipe pressure propagates through the brake pipe at a speed approaching the speed of sound. As this brake pipe pressure reduction passes a particular car, the braking mechanism present on that car is actuated.
Despite the relatively rapid propagation speed of the brake pipe pressure signal, a noticeable time delay may exist in long trains before a pressure reduction initiated in the locomotive will actuate braking mechanisms in cars located at the rear. Because of the this period in which some cars will be in a braking condition while others will not, severe intratrain forces are often present during the braking operation. To reduce these intratrain forces as well as to provide a degree of redundancy, it is desirable to also have the capability of initiating braking at the rear of the train when a braking condition has been commanded in the locomotive.
Recently, many railroads have begun operating freight trains with no attached caboose. When no caboose is used, it is common practice to apply an end-of-train monitor (EOTM) unit to the last car of the train. The EOTM unit will typically transmit data concerning brake pipe pressure to an EOTM cab unit located in the locomotive. Additionally, some EOTM units are capable of initiating a braking condition at the rear of the train when a proper command is received from the EOTM cab unit.
In some cases, a braking condition may be initiated in a railway vehicle even though it has not been requested by the vehicle operator. For example, the locomotive and various cars are typically equipped with emergency braking mechanisms which are responsive to reductions in brake pipe pressure exceeding a predetermined threshold rate. When this rate is exceeded, whether intentionally or unintentionally, brake pipe vent valves automatically open to further facilitate release of brake pipe air to atmosphere. This causes the brake pipe pressure to be reduced by an even greater rate. As this increasing brake pipe pressure reduction is sensed by the various emergency braking mechanisms, an emergency brake application is applied to each railway vehicle. Examples of situations which may initiate an emergency brake pipe reduction in the absence of operator command include a large hole in the brake pipe, a pull-apart of the hose couplings or a faulty emergency mechanism on one of the cars. The current systems utilizing an EOTM monitor, however, have generally been incapable of initiating rear brake venting in the event of such an emergency braking condition.